CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014	Nov. 30, 2014
1 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Interest rate on convertible senior notes	1.00%	1.00%	1.00%	1.00%	1.00%
2 3/4 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Interest rate on convertible senior notes	2.75%	2.75%	2.75%	2.75%	2.75%
Financing activities:
Principal amount repurchased	$ 61.1				$ 140.0	$ 140.0